1. Field of the Invention
The present invention relates to a novel process for preparing 3,5-bis(haloalkyl)pyrazole, especially 3,5-bis(fluoroalkyl)pyrazole derivatives.
2. Description of Related Art
Polyhaloalkylpyrazolylcarboxylic acid derivatives, especially polyfluoroalkylpyrazolylcarboxylic acid derivatives and 3,5-bis(fluoroalkyl)pyrazoles are valuable precursors of active fungicidal ingredients (cf. WO 2003/070705 and WO 2008/013925).
Pyrazolecarboxylic acid derivatives are typically prepared by reacting acrylic acid derivatives having two leaving groups with hydrazines (cf. WO 2009/112157 and WO 2009/106230). WO 2005/042468 discloses a process for preparing 2-dihaloacyl-3-aminoacrylic esters by reacting acid halides with dialkylaminoacrylic esters and subsequent cyclization thereof with alkyl hydrazines. WO 2008/022777 describes a process for preparing 3-dihalomethylpyrazole-4-carboxylic acid derivatives by reacting α,α-difluoroamines in the presence of Lewis acids with acrylic acid derivatives and subsequent reaction thereof with alkyl hydrazines.
3,5-Bis(fluoroalkyl)pyrazoles are prepared by reacting bisperfluoroalkyl diketones (e.g. 1,1,1,5,5,5-hexafluoroacetylacetone) with hydrazines (cf. Pashkevich et al., Zhurnal Vsesoyuznogo Khimicheskogo Obshchestva im. D. I. Mendeleeva (1981), 26(1), 105-7), the yield being only 27-40%. The synthesis, isolation and purification of the polyfluoroalkyl diketones is very complex since the compounds are generally very volatile and highly toxic.